LibSQL: Implement evaluate() method of BinaryOperatorExpression

Mostly just calls the appropriate methods on the Value objects.
Exception are the `Concatenate` (string concat), and the logical `and`
and `or` operators which are implemented directly in
`BinaryOperatorExpression::evaluate`

Userland/Libraries/LibSQL/AST/AST.h

@@ -490,6 +490,7 @@ public:
     }
 
     BinaryOperator type() const { return m_type; }
+    virtual Value evaluate(ExecutionContext&) const override;
 
 private:
     BinaryOperator m_type;